Analysis of ascorbic acid, pH and antioxidants across value to premium range supermarket apple juices at varying temperatures and periods of exposure

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Abstract

Background
Ascorbic acid is an important antioxidant and essential vitamin used as a cofactor for the hydroxylase enzymes for proline and lysine, which are required in the synthesis of collagen (Baum et al, 2010). Antioxidants, such as ascorbic acid, also provide a beneficial biological defence mechanism against free radical damage of important biological compounds, such as DNA (Baum et al, 2010). Apple juice naturally contains low levels of ascorbic acid because of the high levels of malic acid and low pH, although it is often added as preservation (Ballus et al, 2012). However, these values been shown by: Achir et al (2015); and Baum et al (2010), to be dependent on storage conditions and processing method. Methods
Six samples in three price ranges of apple juice were measured for 4-7 days after opening. The antioxidant activity was measured using the DPPH method used by Kedare and Singh (2011), to determine the % radical scavenging activity. Ascorbic acid was analysed by the Iodometric method as well as by kinetic modelling using first and zero order kinetics (Hwa and Sapei, 2011). Results
Medium price range apple juices had significantly more ascorbic acid (p<0.001) and antioxidant content than premium and value ranges. The period of exposure after opening was shown to have an effect on the: ascorbic acid content (p<0.001); antioxidant content (P<0.001) and the pH value (P<0.001). There were no significant differences observed between 4°C and 19°C for: pH, ascorbic acid or the antioxidant activity. Discussion
A similar study taken by Gevilla et al (2011), found that pasteurised apple juice (equivalent to medium price range) contains higher levels of both: antioxidants; and ascorbic acid, than fresh juice (equivalent to premium range). This agreed with the observed result for medium range apple juices for ascorbic acid and Antioxidants. The negative effect of days, on ascorbic acid, was consistent with all 3 of the previous studies analysed (Achir et al, 2015; Ballus et al, 2012; Hwa and Sapei, 2011). Conclusion
In conclusion, despite the expected increased quality from medium to premium range apple juices, medium range apple juices were far more likely to contain beneficial antioxidants, such as ascorbic acid. The significant negative effect of exposure on the ascorbic acid content over the first 4 days, suggests further research is required on juices where this value is labelled on the bottle.

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